Magnetic recording media for VTRs integrated with cameras, particularly for the VHS-C system, have a recording time limit of 30 minutes in the normal mode. In recent year, there are growing expectations for magnetic recording media recordable for a longer period of time. In order to prolong the recording time, it is necessary to make magnetic recording media thinner. In this case, however, the problem is that the mechanical strength characteristics of the media are deteriorated, resulting in tape folding or breakage under repeated running. For solving this problem, some proposals have been made to add chromium dioxide to magnetic layers, thereby improving the mechanical strength characteristics of the media.
That is to say, (1) blending of chromium dioxide in an amount of less than 40% by weight based on the total amount of ferromagnetic powder is proposed in Japanese Examined Patent Publication No. 55-28129, Japanese Examined Patent Publication No. 52-11207, Japanese Examined Patent Publication No. 7-46418, Japanese Unexamined Patent Publication No. 51-149007, Japanese Unexamined Patent Publication No. 57-46326, Japanese Unexamined Patent Publication No. 3-86917 and Japanese Unexamined Patent Publication No. 4-134721, (2) blending of chromium dioxide in an amount of more than 70% by weight based on the total amount of ferromagnetic powder is proposed in Japanese Unexamined Patent Publication No. 49-55303, Japanese Unexamined Patent Publication No. 2-223012, Japanese Unexamined Patent Publication No. 6-176346 and Japanese Unexamined Patent Publication No. 6-208719, (3) blending of chromium dioxide in an amount of 40% to 70% by weight based on the total amount of ferromagnetic powder is proposed in Japanese Examined Patent Publication No. 51-41801, Japanese Unexamined Patent Publication No. 54-161910, Japanese Unexamined Patent Publication No. 60-50727 and Japanese Unexamined Patent Publication No. 60-89823, and (4) the specific amount of chromium dioxide added is not particularly described in Japanese Unexamined Patent Publication No. 60-50725, Japanese Unexamined Patent Publication No. 63-251923, Japanese Unexamined Patent Publication No. 63-271717, Japanese Unexamined Patent Publication No. 3-69013 and Japanese Unexamined Patent Publication No. 3-157811.
In the method of (1) described above, however, the amount of chromium dioxide is less than 40% by weight based on the total amount of ferromagnetic powder, so that sufficient mechanical strength characteristics (dynamic buckling strength) can not be obtained in tapes for long recording (particularly, 40 minutes in the normal mode of the VHS-C system) to raise the problem of occurrence of tape damage. Further, in the method of (2) described above, the amount of chromium dioxide is more than 70% by weight based on the total amount of ferromagnetic powder, which causes an increase in head abrasion loss. Furthermore, in (1) to (4) described above, all methods for preparing paints for magnetic layers are not studied considering the filling properties of the magnetic layers, and measures to obtain the sufficient mechanical strength characteristics in tapes for long recording are not sufficient.